1. Field of the Invention
The invention relates generally to gas filters and purifiers and more specifically to devices that remove both particles and chemical impurities from gases used to fabricate integrated circuits in the semiconductor industry.
2. Description of the Prior Art
Semiconductor processing requires the use of a wide variety of gases in the fabrication process. The conductivity of semiconductor materials is controlled by the careful introduction of certain impurities, such as phosphorus and boron. Unwanted impurities, or even the right ones in the wrong amounts, can spoil all the semiconductor wafers subject to the contamination. Semiconductor manufacturers go to great lengths to buy pure silicon ingots, design and operate class 100, class 10, and class 1 cleanrooms, and even require personnel to wear lint-free "bunny suits" to reduce the risk of contamination.
Gas producers take great care to supply contamination-free gases, but contaminants inevitably creep in. The semiconductor industry therefore customarily uses filters and purifiers at the point-of-use near where the gas is actually used in the process. As such, space is at a premium. Available space is also shrinking with successive generations of equipment as the tools that use them are getting smaller and smaller. Periodic replacement of both filters and purifiers is needed, and this requires that connectors and valves be included and the filters and purifiers located so as to accommodate service. Both the valves and the location needs consume more valuable space.
Several manufacturers worldwide produce a range of purifiers that use various purifying agents internal to the devices. SAES Pure Gas (San Luis Obispo, Calif.) produces a purifier that uses a gettering alloy that must be heated during operation. Japan Pionics, Nippon Sanso, Advanced Technology Materials, Inc. (New Milford, Conn.), and Ergenics (Wyckoff, N.J.) also make commercially available purifiers. Matheson Electronics Product Group, Semi-Gas Division (San Jose, Calif.), produces a line of purifiers that are filled with a highly reactive resin that is commercially marketed as NANOCHEM.RTM. on license from Hercules Corporation. The NANOCHEM resin does not require heating during use and is much less expensive to operate than the types that do require heating. The NANOCHEM, however, must be protected from exposure to air and it is crucial that none of the resin material come close enough to the process of welding a purifier closed to cause the NANOCHEM to melt, because the melting can release enough contaminants to saturate the remaining resin in the purifier.
As integrated circuit semiconductor device geometries decrease, the purification of gases used in fabrication needs to be closer to the point of use. The number of conventional filter-purifiers is limited in such applications. Some otherwise acceptable filter-purifiers are only available in a gland-to-gland dimension of 3.31 inches and have unacceptably low flow rates. Many prior art devices are, at times, difficult to install, because they have an outer radius of 0.75 inches, which is more than the port-center-to-back dimension of the majority of mass flow controllers (MFCs) that they are used with. Standoff brackets are often required to raise the MFCs and other manifold components to accommodate such filter-purifiers.
Equipment gas manifolds are increasingly using smaller footprints. A modular block approach to purification is needed for such applications and to allow for the constant trend toward smaller gland-to-gland and vertical height dimensions.